Afterburner flame stabilization means



AFTERBURNER FLAME STABILIZATION MEANS Filed March 5, 1954 July 23, 1957 FIG. 3

46 0 INVENTOR 'EARL n. com/w BY MJM ATTORNEYS United States Patent AFTERBURNER FLAME STABILIZATION MEANS Earl W. Conrad, Berea, Ohio Application March 5, 1954, Serial No. 414,520

4 Claims. (Cl. 6039.72)

(Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of American for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to improvements in gas reaction engines, and particularly to a device for providing a strong, stable pilot for a jet engine afterburner.

An object of this invention is to provide means for establishing a very strong, stable piloting action for use in turbojet engine afterburners under conditions, such as extremely low pressure or high velocity, at which present afterburner designs will not operate with good efliciency.

Another object of the invention is to provide an afterburner pilot burner which serves as a strut for mechanical support in the engine, and which taps a portion of the extremely hot gas at the engine turbine inlet for combining with fuel and igniting by shock or auto ignition whereby there is always present a dependable pilot for the engine afterburner.

Other objects and features will become apparent in following the description of the illustrated form of the invention.

In the drawing:

Fig. 1 is a fragmentary schematic view of a turbo jet engine having the invention therein.

Fig. 2 is an enlarged sectional view taken on the line 22 of Fig. 1.

Fig. 3 is a perspective view of a typical embodiment of the invention, parts being broken away to show internal details.

The axial flow, turbo jet engine includes an engine casing 12 in which there is a core structure having a diffuser inner body 14. An afterburner 15 is schematically illustrated in casing 12, as is the turbine 18, these elements of the engine being disposed in their usual functional arrangement.

At very low pressure-high velocity conditions of operation, afterburners do not operate satisfactorily. In order to correct this, the invention provides means assuring stable primary burning, which is a requirement for stable operation of the afterburner as a whole. Strut is one instrumentality by which the invention may be practiced, and it consists of an outer shell 22 in which there is an inner shell 24 serving as a gas conductor. Outer shell 22 is secured to the engine casing 12 and the diffuser body 14, holding the latter assembled in shell 22. Any number of struts 20 may be used in an engine, depending on the demands of the particular engine.

As seen in Fig. 1, a by-passpassageway 26 feeds a small amount of the extremely hot gas from the region in advance of turbine 18 to the inner shell 24, the gas entering the chamber 28 through discharge opening 30 in gas conductor 24. Chamber 28 is formed by the spaced walls of shells 22 and 24, and the upper and lower spacers 32 which help to hold the shells assembled. There is a discharge opening 36 at the aft end of shell 22, and it is in communication with chamber 28 through a convergingice diverging passage 38 on each side of strut 20 and bounded by the walls of the inner and outer shells 24 and 22 respectively.

Means are provided for delivering fuel to the gas as it passes through strut 20, a suggested arrangement being shown in Fig. 1 where a line 40 is taken from the afterburner fuel supply system and led into the strut. The fuel line 40 is connected to two ducts 42 and 44, one being fixed to each side of inner shell 24. A series of orifices 46 are formed in the inner shell walls, opening into the interior of ducts 42 and 44 so that fuel may be delivered through the inner shell walls and into passage 38 to admix with the gas passing therethrough.

There is a grid 48 in the discharge opening 36 comprised of a series of plates placed parallel to the direction of the airstream, and a plurality of generally V-shaped gutters 50 carried by the outer shell 22. The gutters are located at opening 36, extend rearwardly of strut 20, and then diverge. The purposes of grid 48 and gutters 50 will be stated subsequently.

In operation, a portion of the extremely hot gas at the turbine inlet is by-passed around turbine 18 through passage 26 and introduced into gas conductor 24 which is in registry with passage 26. The gas flows through opening 30, chamber 28, passageway 38, and finally through discharge opening 36. A portion of the afterburner fuel is injected into the hot gas as it passes through the passageway 38, and it ignites by auto ignition, thereby avoiding the need for any other ignition device. Excellent combustion in the afterburner region is assured in View of the high dependability of the hot shot pilot system which ignites fuel by auto ignition at the same temperature but at much higher velocities than those existing in the strut 20.

The gutters 50 serve to stabilize the combustion of the main afterburner fuel not only by the mechanism of recirculation but also by the spread of the primary burning from the strut along the sheltered regions provided by the gutters.

The illustrated embodiment may exploit the high reaction rates possible with shock ignition. The passage 38 is in the form of a converging-diverging nozzle which accelerates the gas flow sufticiently to form a standing shock. The flame would seat on this standing shock front. The low solidity grid 48 (i. e., a series of parallel plates having a low proportion of the total frontal area thereof taken up by the plates) is preferably placed adjacent the trailing edge of airfoil-shaped conduit 24 and is intended to produce bow waves (shock waves ahead of the plates of the grid 48 which would intersect and reinforce, increasing the temperature Within the shock. Grid 48 is optionally used, regardless of whether there is auto ignition or shock ignition in the engine afterburner region.

It is understood that various modifications may be made without departing from the following claims.

What is claimed is:

1. In combination, an engine casing, a diffuser inner body, struts holding said casing and said body in spaced assembled relationship, at least one of said struts comprising a shell having a rounded leading edge, an airfoilshaped conduit within said shell, means connecting said conduit to a source of high-temperature gas, outlet means in said conduit directed toward the interior of said leading edge, pipe means within said conduit, said pipe means being connected to a source of fuel, outlet means for said fuel in said pipe and in said conduit downstream of said first mentioned outlet means, and an opening in said strut opposite said leading edge.

2. The apparatus of claim 1, and grid means in said strut opening adjacent the trailing edge of said airfoilr a "4 a shaped conduit to produce intersecting and reinforcing 1 References Cited in the file of this patent bow Waves in the region between said shell and said con- UNITED STATES PATENTS duit. a

3. Apparatus as in claim 1, said one strut extending 2482505 Plerce Sept 1949 'rearwardly fiom said leading edge and forrniuga' cdn- 5 2673445 Bruckmann 1954 verging-diverging nozzle with said airfoil l'shafied'conduit. 2674845 Pouchot 1954 4. The apparatus of claim 1, and a grid in said strut opening, said grid comprising a series ofpl ates parallel to FOREIGN PATENTS V a 7 r 499,468 Belgium Mar. 16, 1951 the direction of the airstream. V I 

